To date, wide utilization in tightening coarse thread connections have found numerous means and devices ranging from simple wrenches and power drive bolt tightening machines to cranes or derricks.
For tightening a threaded connection use is generally made of prestraining of a threaded piece, such as a stud piece, of the connection by means of a hydraulic jack or by heating thereof with consequent screwing the nuts. However, the above means and machines lack convenience in operation, are cumbersome and require the use of additional equipment to be employed in conjunction with such hydraulic jacks or for preheating of the threaded piece of the connection.
Known in the art are devices for tightening coarse thread connections as exemplified in USSR Inventors' Certificates Nos. 258,157 and 344,980; Cl. B 25 b 29/02, published Nov. 20, 1969 and July 14, 1972 respectively.
Either of the above devices comprises a pressure element adapted to thrust against one of the pieces to be connected, a tension element having a wedge groove accommodating a power wedge intended to act upon the pressure element to produce strain in the threaded piece, such as a fastening bolt or a stud. The power wedge is a one-way action type, that is one working surface thereof is straight or vertical, whereas another one is inclined, the angle of inclination between the surfaces ranging between 1.degree. and 7.degree. depending on the required operational parameters.
The power wedge is essentially of a rectangular cross-section with side or non-working surfaces thereof being straight or vertical. A screw drive is employed to effect displacement of the power wedge along the groove of the tension element, the screw drive being disposed in the tension element. The tension element is made integral with a head of the fastening bolt. In order to form the wedge groove, wherein the power wedge moves, the pressure element is provided with an inclined surface and accommodated in the groove of the tension element, the inclined surface of the power wedge cooperating with the inclined surface of the pressure element.
The aforedescribed devices afford to produce, at high torques exerted to the nut of the fastening bolt and therefore at high axial loads, the same value of the axial load with dozens of times lesser torques applied, which is to some extent advantageous in operation. However, these devices can only be used as stationary devices, that is they must be provided at every fastening bolt to be tightened. Accordingly, they are preferably to be used in conjunction with flange connections or couplings which are subject to frequent dismantling, such as those dismantled several times within one week.
The use of the above devices for flange connections which are not subject to frequent disassembling is economically unjustified, since each fastening bolt should be provided with such ancillaries as a wedge, screw, pressure element and other extra parts. Also, these devices fail to effect repeated tightening of a threaded connection with a view to attain a rated load to be exerted to a bolt or stud.
Further known is a detachable means for tightening threaded connections which can be removed from one tightened connection to be used for tightening another connection (cf. Patent of Germany, Federal Republic of, No. 2,238,974; Cl. B 25 B 23/14, published Dec. 12, 1974). A pressure element in this device is fashioned as a body embracing both a tension element and a nut of a stud piece to be connected. For imparting tension to the stud piece use is made here of an eccentric shaft acting through a sleeve member on the tension element and exerting pressure against the pressure element through rollers. Also, there is provided a lever or bar secured to a square head at the ends of the eccentric shaft. This device, however, can be used only with threaded connections of one size. In addition, for fastening, i.e. screwing, the tension element to the end of the piece to be tightened it is necessary to rotate the whole device together with the eccentric shaft and lever which to some extent limits the range of application of the device, since sufficient room must be available around the piece to be tightened. Further, the eccentric shaft creates considerable specific pressures on the cooperating surfaces, which results in undue wear thereof and leads to an increase in the value of torque applied thereto.
Employment in the heretofore described device of a mechanism other than the eccentric shaft, for example, of a wedge driven by a screw, will fail to expand the range of application or the operating principle thereof.